Optical disc player

ABSTRACT

A method of detecting the type of optical disc inserted in an optical disc player including the steps of: 
     i) attempting to focus a laser read head on the disc using a first set of player parameters appropriate for a first type of disc; 
     ii) if focus is obtained: 
     a) reading data from the disc and determining whether a sub-code representative of a second type of disc is present; 
     b) if so changing the first set of player parameters to a second set of player parameters appropriate to a second type of disc; 
     c) if not playing or indicating the presence of the first type of disc; 
     iii) if focus is not obtained changing the first set of player parameters to the second set of player parameters; 
     iv) if focus is then found playing or indicating the presence of the second type of disc.

The invention relates to an optical disc player and to a method ofdetecting different types of optical disc inserted into the player.

Various types of optical discs are known which have been developedaccording to different standards for the recording and/or replay ofdata. This data may represent audio or video signals or may be puredata. High reflectivity discs, which may typically be CD Audio, CDROM,DVD, or CD recordable, often referred to as write once read many (WORM),generally produce a reflected signal which is of relatively largeamplitude. Re-recordable discs, which may typically be CD-RW or CDRAM,however, generally have a lower reflectivity and consequently thereflected signal will have a lower amplitude. As a result, in order tooptimise the decoding of the data on the discs it is desirable toprovide different parameters for the detection circuits within theplayer for the different types of disc.

Generally optical disc players are set to focus on a high reflectivitydisc and if focus is not found, that is the reflected signal does notreach a preset threshold level, then the player parameters are changedon the assumption that a low reflectivity disc is present. An attempt isthen made to focus using parameters appropriate to a low reflectivitydisc. If focus is still not found an indication is given that noplayable disc is present. This procedure has been published inEP-A-0789354 and is satisfactory provided that the player does not focuson a low reflectivity disc when using parameters appropriate for highreflectivity discs. Initial focussing is generally attempted when thedisc is stationary in the player. It has been discovered that underthese comparatively ideal conditions some nominally low reflectivitydiscs may allow focus to be achieved since the detected reflected signalmay marginally exceed the threshold value set. When, however, the discis rotated there is then insufficient noise margin to allow the data tobe reliably read from the disc particularly when jumps from one radialposition to another are performed. In addition the rotation of the discis controlled by a digital phase locked loop (DPLL) working on the dataread from the disc and if the data is not read correctly the DPLL maylose phase or frequency lock resulting in the spinning out of control.

In this specification non-recordable discs include high reflectivityWORM type discs in addition to those which are preformed and unable torecord any data.

It is an object of the invention to enable the provision of an opticaldisc player that is able to discriminate more reliably between differenttypes of disc so that it can more reliably read data from differenttypes of disc.

The invention provides a method of detecting the type of optical discinserted in an optical disc player comprising the steps of;

i) attempting to focus a laser read head on the disc using a first setof player parameters appropriate for a first type of disc,

ii) if focus is obtained

a) reading data from the disc and determining whether a sub-coderepresentative of a second type of disc is present,

b) if so changing the first set of player parameters to a second set ofplayer parameters appropriate to a second type of disc,

c) if not playing or indicating the presence of the first type of disc,

iii) if focus is not obtained changing the first set of playerparameters to said second set of player parameters,

iv) if focus is then found playing or indicating the presence of thesecond type of disc.

By attempting to read data which is only present on re-recordable discs,hereinafter referred to as read-write discs it can be ensured thatread-write discs are read using player parameters appropriate to lowerreflectivity discs regardless of whether the player was able toinitially focus on the disc using the parameters appropriate for highreflectivity non-recordable discs. This has the advantage thatread-write discs of comparatively high reflectivity, but not as high asnon-recordable discs, can be reliably identified and the playeroptimised for their playback rather than attempting to use the wrong setof parameters merely because focus was originally found. An alternativesolution would have been to increase the threshold required forobtaining focussing of high reflectivity non-recordable discs but thiswould have the disadvantage of possible failure to focus on lowerreflectivity non-recordable discs.

Step ii) a) may be performed by reading a table of contents anddetermining whether mode 5 sub-code is present in the Q sub-codechannel. Read-write discs conforming with part 3 of the Orange BookStandard contain a mode 5 sub-code and in this way relatively highreflectivity read-write discs on which the player may be able to focuswhen the disc is stationary but where it may lose focus when the disc isspinning or when the read head jumps from one position to another acrossa plurality of tracks can be identified. The appropriate measures canthen be taken to alter the player parameters to more reliably maintainfocus and read the data

The method may further comprise when focus is found in step iv) thesteps of;

vi) reading data from the disc, and

vii) determining whether mode 5 sub-code is present before indicatingthe presence of the second type of disc.

In this way it can be ensured that it is a recordable disc being playedrather than a low reflectivity non-recordable disc.

If focus is not found in step iv) then the method may further comprisethe step of;

v) indicating that no playable disc is present.

The player parameters may comprise the gain of an amplifier forming partof a data tracking loop and/or a sensitivity control for processingindividual diode outputs from the read head.

The invention further provides an optical disc player capable ofdetecting the type of disc loaded in the player comprising means forsetting a first set of player parameters appropriate for playing discsof a first type, means for focussing the read head on the disc, meansfor reading data from the disc, means for processing the data anddetecting the presence of a sub-code representative of a second type ofdisc, means for setting a second set of player parameters appropriatefor playing a disc of a second type if the sub-code is present, andmeans for setting the second set of parameters if focus is not foundusing said first set of parameters.

The optical disc player may further comprise means for indicating thatno readable disc is present if focus is not obtained using either thefirst or second set of parameters.

The sub code representative of the second type of disc may be a mode 5sub-code in the Q sub-code channel. Such sub-codes are always present inCD-RW discs conforming with part 3 of the Orange Book Standard and serveas a means of detecting the presence of such discs regardless of whethertheir reflectivity is sufficiently high that the player can focus onthem using parameters optimised for high reflectivity CD Audio or CDROMdiscs.

The gain of a high frequency amplifier which amplifies the sum of thediode outputs from the read head may be increased for low reflectivityread-write discs. Alternatively or in addition the sensitivity of ananalogue to digital converter block to which individual diode outputsare applied may be increased for low reflectivity recordable discs.

The above and other features and advantages of the invention will becomeapparent from the following description, by way of example, ofembodiments of the invention with reference to the accompanyingdrawings, in which;

FIG. 1 shows in block schematic form the servo control system of anoptical disc player which incorporate the invention, and

FIG. 2 is a flow diagram illustrating a method according to theinvention.

As shown in FIG. 1 the servo control system for an optical disc playeraccording to one embodiment of the invention comprises a conventionallaser mechanism 1 which contains an illuminating laser and associatedoptics for focussing the laser on the information surface of an opticaldisc. The laser mechanism 1 also includes appropriate detectors fordetecting the radiation reflected from the disc in order to producesignals representing the data and indicating tracking of the informationtracks. Also included is a motor for rotating the disc, means forfocussing the laser radiation on selected portions of the disc undercontrol of signals generated within the servo control system, and meansfor moving the reading head radially across the disc.

Four outputs D1-D4 from the laser mechanism 1 are summed in a summer 2and fed to a high frequency amplifier 3. The four outputs D1-D4 togetherwith two further outputs R1 and R2 are fed to an analogue to digitalconverter block 4, the output of which is passed to a pre-processingblock 5 and then to a PID controller 6. A first output of the PIDcontroller 6 is fed to a focus detector 7, while a second output is fedto an output stage 8 which produces outputs to control the focussing ofthe laser on the disc (FO), the fine radial positioning of the laserhead on the disc (RA), and the sledge position (SL) which provides acoarse positioning of the read head with respect to tracks on the disc.The three outputs of the output stage 8 are fed through power amplifiers9 to the laser mechanism 1. The output of the focus detector 7 is fedvia an interface 10 to a controlling microprocessor 11.

The output of the amplifier 3 is fed to a front end circuit 12 whichslices and converts the signal so that it is in the required form forapplication to a digital phase locked loop (DPLL) 13, an output of whichis fed to a motor control circuit 14 which controls the speed of thespindle motor to cause the disc to be rotated at the desired speed forcorrect reading of the data from the disc. The output of the motorcontrol circuit is fed through the power amplifiers 9 to the spindledrive motor. The controlling microprocessor produces a signal CDRW thatis arranged to vary the gain of the amplifier 3 according to whether adisc having high reflectivity, that is a CD Audio, CDROM, DVD, or thelike, or a disc having a low reflectivity, that is a CD-RW, CDRAM, orthe like. Thus the gain of the amplifier is increased when a lowreflectivity disc is being played as the received signal will have alower amplitude than one received from a high reflectivity disc. Inaddition the microcontroller 11 increases the sensitivity of theanalogue to digital converter block 4 to compensate for the lower levelsof the signals D1-D4, R1, and R2. Thus far the servo control system isconventional and is constructed from well known circuit elements used inoptical disc players.

The servo control system also includes a sub-code processor 15 thatreceives data read from the disc via the DPLL 13 and inspects this datafor the presence of particular sub-codes. As set forth in part 3 of theOrange Book Standard for CD-RW discs lead in information is encoded inthe Sub-code Q channel. For CD-RW discs sub-code mode 5 is alwayspresent. By detecting this sub-code, the player is able to distinguishbetween high reflectivity non-recordable discs and read-write discshaving a comparatively high reflectivity which may be sufficient toenable a focus indication to be achieved even when a CD-RW disc isinserted in the player. This, of course, would not be necessary if thedata from the CD-RW disc could be reliably read using the parameterssuitable for non-recordable discs. It is found, however, that while itmay be possible to focus on the disc when it is stationary, focus may belost when the disc starts spinning or when the reading head jumps fromone radial position to another. During this process it is necessary tomaintain focus in order to count the track crossings so that the finalposition can be determined. If the mode 5 sub-code is present thesub-code processor sends a signal to the control processor 11 via theinterface 10. This signal causes the control processor 11 to produce anoutput CDRW that is fed to the amplifier 3 to increase its gain. Inaddition the control microprocessor will adjust the sensitivity of theanalogue to digital converter block4 via the interface 10. As a resulteven if focus is detected using parameters appropriate for a highreflectivity disc the parameters can be reset on detection of the mode 5sub-code to those appropriate for a low reflectivity CD-RW disc.

FIG. 2 is a flow diagram illustrating a method according to theinvention for identifying the type of disc loaded into an optical discplayer. As shown in FIG. 2 the method starts, step 201, with theinsertion of a disc into the player. The next step of the method, step202, is to attempt to focus the laser beam on the disc using parametersappropriate for high reflectivity non-recordable discs. A check is thenmade, decision 203, as to whether focus has been attained by determiningwhether the reflected signal reaches a preset threshold value. If, atstep 203, focus is obtained the disc is then started, that is thespindle motor is started to rotate the disc, step 204. An attempt isthen made to read the table of contents, step 205. A check is then made,decision 206, as to whether the table of contents has been read and, ifso, then the sub-code Q channel is examined to look for mode 5 sub-codeidentifying a CD-RW disc. A check is then made to determine whether mode5 is present, decision 208. If so, then the parameters are changed tothose appropriate to CD-RW or other relatively low reflectivity discs,step 209. Thus the gain of amplifier 3 is increased and the sensitivityof the analogue to digital converter block 4 is increased. The procedurethen ends, step 210. If the mode 5 sub-code is not detected then it isassumed that a high reflectivity disc is present and the initialparameters are retained.

If, at step 203, focus is not obtained then a check is made as towhether the parameters have been changed to those appropriate for lowreflectivity discs, decision 211. If not then the parameters are thenchanged, step 212, and a further attempt to obtain focus is made, step213. If the attempt is now successful, decision 214, the procedurereverts to the input of step 204 and the disc is started and an attemptis made to read the table of contents and identify the mode 5 sub-code.

If it is not possible to read the table of contents, output NO ofdecision 206, then the process branches to the input of decision 211where it is decided whether the parameters have already been changed tothose appropriate to low reflectivity discs. If the parameters have beenchanged, output YES of decision 211, then an indication that no readabledisc is present is generated, step 215. Further if focus can not beobtained after the parameters have been changed to those appropriate tolow reflectivity discs, output NO of decision 214, then the proceduregoes to step 215 and an indication that no readable disc is present ismade.

It will be apparent from the foregoing that by monitoring the table ofcontents to detect whether mode 5 sub-code is present it can be ensuredthat a CD-RW disc is detected and the player parameters can be modifiedto reliably read the data from the disc. Other codes may be applicableto other forms of low reflectivity discs according to standards otherthan that set forth in the Orange Book Standard. In general any codewhich identifies the disc as being of relatively low reflectivity can beidentified by appropriate decoding means and used to check for thepresence of such a disc and when found to modify the parameters of theplayer to optimise reading of the disc. It will be clear that thismethod is particularly advantageous for identifying discs which aremarginally above the reflectivity necessary to obtain focus when thedisc is stationary but not sufficiently above that level to enable focusto be maintained under dynamic condition.

From reading the present disclosure, other modifications will beapparent to persons skilled in the art. Such modifications may involveother features which are already known in the design and use of opticaldisc players and component parts thereof and which may be used insteadof or in addition to features already described herein. Although claimshave been formulated in this application to particular combinations offeatures, it should be understood that the scope of the disclosure ofthe present application also includes any novel feature or any novelcombination of features disclosed herein either explicitly or implicitlyor any generalisation of one or more of those features which would beobvious to persons skilled in the art, whether or not it relates to thesame invention as presently claimed in any claim and whether or not itmitigates any or all of the same technical problems as does the presentinvention. The applicants hereby give notice that new claims may beformulated to such features and/or combinations of such features duringthe prosecution of the present application or of any further applicationderived therefrom.

What is claimed is:
 1. A method of detecting the type of optical discinserted in an optical disc player comprising: i) attempting to focus alaser read head on the disc using a first set of player parametersappropriate for a first type of disc; ii) if focus is obtained: a)reading data from the disc and determining whether a sub-coderepresentative of a second type of disc is present; b) changing thefirst set of player parameters to a second set of player parametersappropriate to a second type of disc, when the second type of disc isdetermined; c) playing or indicating the presence of the first type ofdisc, when the second type of disc is not determined; iii) if focus isnot obtained, changing the first set of player parameters to the secondset of player parameters, and attempting to focus using the second setof player parameters; and iv) if focus is then found, playing orindicating the presence of the second type of disc.
 2. The method ofclaim 1 in which the reading of data includes reading a table ofcontents and determining whether a mode 5 sub-code is present in a Qsub-code channel.
 3. An optical disc player capable of detecting thetype of disc loaded in the player comprising: means for setting a firstset of player parameters appropriate for playing discs of a first type;means for focusing the read head on the disc; means for reading datafrom the disc if focus is found; means for processing the data anddetecting the presence of a sub-code representative of a second type ofdisc; means for setting a second set of player parameters appropriatefor playing a disc of a second type if the sub-code is present; andmeans for setting the second set of parameters if focus is not foundwhen using the first set of parameters.
 4. The player of claim 3 furthercomprising means for indicating that no readable disc is present iffocus is not found using either the first or second set of parameters.5. The method of claim 1 in which if focus is not found using the secondset of player parameters then the method further comprises the step of;v) indicating that no playable disc is present.
 6. The method of claim 1in which if focus is found using the second set of player parametersthen the method further comprises: vi) reading data from the disc; andvii) determining whether the sub-code representative of the second typeof disc is present before indicating the presence of the second type ofdisc.
 7. The method of claim 1 in which the player parameters includethe gain of an amplifier forming part of a data-tracking loop.
 8. Themethod of claim 7 in which the player parameters include a sensitivitycontrol for processing individual diode outputs from the read head. 9.The method of claim 1 in which: if focus is not found using the secondset of player parameters then the method further comprises: v)indicating that no playable disc is present; if focus is found using thesecond set of player parameters then the method further comprises: vi)reading data from the disc; and vii) determining whether the sub-coderepresentative of the second type of disc is present before indicatingthe presence of the second type of disc; the player parameters includethe gain of an amplifier forming part of a data-tracking loop; and theplayer parameters include a sensitivity control for processingindividual diode outputs from the read head.
 10. The player of claim 3in which the sub code representative of the second type of disc is amode 5 sub-code in a Q sub-code channel.
 11. The player of claim 3 inwhich the gain of a high frequency amplifier which amplifies the sum ofthe diode outputs from the read head is increased for low reflectivityrecordable discs.
 12. The player of claim 3 in which the sensitivity ofan analogue to digital converter block to which individual diode outputsare applied is increased for low reflectivity recordable discs.
 13. Theplayer of claim 3 in which: the sub code representative of the secondtype of disc is a mode 5 sub-code in a Q sub-code channel; the gain of ahigh frequency amplifier which amplifies the sum of diode outputs fromthe read head is increased for low reflectivity recordable discs; andthe sensitivity of an analogue to digital converter block to whichindividual diode outputs are applied is increased for low reflectivityrecordable discs.